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Artist’s concept of a Kepler-1658-like system. Sound waves propagating through the stellar interior were used to characterize the star and the planet. Kepler-1658b, orbiting with a period of just 3.8 days, was the first exoplanet candidate discovered by Kepler nearly 10 years ago. Image Credit: Gabriel Perez Diaz/Instituto de Astrofísica de Canarias

March 5, 2019 – An international team of astronomers, led by University of Hawaiʻi graduate student Ashley Chontos, announced the confirmation of the first exoplanet candidate identified by NASA’s Kepler Mission. The result was presented today at the fifth Kepler/K2 Science Conference held in Glendale, California.

Launched almost exactly 10 years ago, the Kepler Space Telescope has
discovered thousands of exoplanets using the transit method – small dips
in a star’s brightness as planets cross in front of the star. Because
other phenomena can mimic transits, Kepler data reveal planet
candidates, but further analysis is required to confirm them as genuine
planets.

Despite being the very first planet candidate discovered by NASA’s
Kepler Space Telescope, the object now known as Kepler-1658 b had a
rocky road to confirmation. The initial estimate of the size of the
planet’s host star was incorrect, so the sizes of both the star and
Kepler-1658 b were vastly underestimated. It was later set aside as a
false positive when the numbers didn’t quite make sense for the effects
seen on its star for a body of that size. Fortuitously, Chontos’ first
year graduate research project, which focused on re-analyzing Kepler
host stars, happened at just the right time.

“Our new analysis, which uses stellar sound waves observed in the
Kepler data to characterize the host star, demonstrated that the star is
in fact three times larger than previously thought. This in turn means
that the planet is three times larger, revealing that Kepler-1658 b is
actually a hot Jupiter-like planet,” said Chontos. With this refined
analysis, everything pointed to the object truly being a planet, but
confirmation from new observations was still needed.

“We alerted Dave Latham (a senior astronomer at the Smithsonian
Astrophysical Observatory, and co-author on the paper) and his team
collected the necessary spectroscopic data to unambiguously show that
Kepler-1658 b is a planet,” said Dan Huber, co-author and astronomer at
the University of Hawaiʻi. “As one of the pioneers of exoplanet science
and a key figure behind the Kepler mission, it was particularly fitting
to have Dave be part of this confirmation.”

Kepler-1658 is 50% more massive and three times larger than the Sun.
The newly confirmed planet orbits at a distance of only twice the star’s
diameter, making it one of the closest-in planets around a more evolved
star – one that resembles a future version of our Sun. Standing on the
planet, the star would appear 60 times larger in diameter than the Sun
as seen from Earth.

Planets orbiting evolved stars similar to Kepler-1658 are rare, and
the reason for this absence is poorly understood. The extreme nature of
the Kepler-1658 system allows astronomers to place new constraints on
the complex physical interactions that can cause planets to spiral into
their host stars. The insights gained from Kepler-1658b suggest that
this process happens slower than previously thought, and therefore may
not be the primary reason for the lack of planets around more evolved
stars.

“Kepler-1658 is a perfect example of why a better understanding of
host stars of exoplanets is so important.” said Chontos. “It also tells
us that there are many treasures left to be found in the Kepler data.”

A preprint of the paper, entitled “The Curious Case of KOI 4:
Confirming Kepler’s First Exoplanet Detection,” by Chontos et al. is
available for download here. It has been accepted for publication in the Astronomical Journal.